Planar distributed element antenna isolation board

ABSTRACT

An antenna isolation circuit, meter reading device, and method of manufacturing an antenna isolation circuit are disclosed herein. A multilayer planar structure antenna isolation circuit uses distributed elements to provide high voltage isolation and RF coupling functions. The distributed elements may be implemented, for example, as multilayer distributed capacitors. In other embodiments, the distributed elements may be implemented as a distributed transformer.

TECHNICAL BACKGROUND

The reading of electrical energy, water flow, and gas usage hashistorically been accomplished with human meter readers who came on-siteand manually documented meter readings. Over time, this manual meterreading methodology has been enhanced with walk by or drive by readingsystems that use radio communications to and from a mobile collectordevice in a vehicle. Recently, there has been a concerted effort toaccomplish meter reading using fixed communication networks that allowdata to flow from the meter to a host computer system without humanintervention.

Utility meters that use radio communications to send data to and receivedata from a mobile collector device include antennas for emitting radiosignals and for receiving radio signals from the mobile collectordevice. In a typical utility meter, an antenna isolation board provideshigh voltage isolation between external antenna components and meterline voltages. Insufficient high voltage isolation may compromise thesafety of the utility meter by potentially exposing a user who touchesthe antenna to the line voltage that powers the utility meter. Inaddition, insufficient high voltage isolation may adversely affect theperformance of the utility meter by leaving the internal components ofthe utility meter vulnerable to electrical discharges to the antenna,e.g., during electrical storms.

In order to satisfy commonly accepted industry specifications, theantenna isolation board should provide at least 5 kV of voltageisolation between the antenna or an antenna cable attached to theantenna and any internal components of the utility meter, including, forexample, a radio frequency (RF) port. Additionally, the antennaisolation board should provide a low loss RF path between the antennacable and the RF port over the entire operating frequency range.Further, it is desirable for the antenna isolation board to offerelectrostatic discharge (ESD) protection for the internal components ofthe utility meter by presenting a low impedance across the antenna cableterminals for voltage transients induced on the antenna or antennacable.

In some conventional utility meters, the antenna isolation board isimplemented using high voltage capacitors and a shunt element, such asan inductor or a resonant stub. The capacitors provide voltage isolationbetween antenna coaxial and radio RF connections. The shunt elementprovides ESD and transient protection for the RF input. This type ofcircuit can provide satisfactory RF performance, but the high voltagecapacitors required for implementing the circuit are relativelyexpensive. Further, it is usually necessary to apply a dielectricovercoating to the capacitors and the areas surrounding the capacitorsto meet voltage isolation requirements due to the small terminalspacings for available capacitors. Applying the dielectric overcoatinggenerally involves a manual secondary process. Normal applicationvariances can cause substantial variability in the antenna board voltageisolation and RF performance.

Accordingly, a need exists for an antenna isolation board that provideshigh voltage isolation between an antenna or antenna cable and theinternal components of a utility meter while avoiding the shortcomingsof conventional implementations.

SUMMARY OF THE DISCLOSURE

An antenna isolation circuit, meter reading device, and method ofmanufacturing an antenna isolation circuit are disclosed herein.According to various embodiments, a printed circuit board antennaisolation circuit uses distributed elements to provide high voltageisolation and RF coupling functions. The distributed elements may beimplemented, for example, as multilayer distributed capacitors. In otherembodiments, the distributed elements may be implemented as adistributed transformer.

One embodiment is directed to an antenna isolation circuit. The antennaisolation circuit includes a multilayer planar structure comprising atleast two conductive layers separated from one another by a dielectricmaterial. A first radio frequency port is electrically connected to themultilayer planar structure and is arranged to be electrically connectedto an antenna. A second radio frequency port is electrically connectedto the multilayer planar structure and is arranged to be electricallyconnected to a radio circuit receiving power from a power source. Adistributed circuit element is electrically connected to the first radiofrequency port and to the second radio frequency port and includes atleast some of the conductive layers of the multilayer planar structure.The distributed circuit element is configured to electrically isolatethe antenna from the power source when the antenna is electricallyconnected to the first radio frequency port and the radio circuit iselectrically connected to the second radio frequency port.

Another embodiment is directed to a meter reading device comprising apower source, a metering circuit configured to measure consumption of aresource, a transceiver electrically connected to the metering circuitand configured to generate a signal based on the measured consumption ofthe resource, an antenna operatively coupled to the transceiver andconfigured to emit the generated signal, and an antenna isolationcircuit electrically connected to the transceiver and to the antenna.The antenna isolation circuit includes a multilayer planar structurecomprising a plurality of layers. At least some of the layers of themultilayer planar structure have respective conductive traces. Adielectric material separates each of the plurality of layers.Distributed circuit elements are electrically connected to thetransceiver and to the antenna and comprise the respective conductivetraces of at least some of the layers of the multilayer planarstructure. The distributed circuit element is configured to electricallyisolate the antenna from the power source.

According to yet another embodiment, a method of manufacturing anantenna isolation circuit involves providing a multilayer planarstructure comprising a plurality of conductive layers separated by adielectric material. A first radio frequency port is provided that iselectrically connected to the multilayer planar structure and arrangedto be electrically connected to an antenna. A second radio frequencyport is provided that is electrically connected to the multilayer planarstructure and is arranged to be electrically connected to a radiocircuit. A distributed circuit element is formed as conductive traces onat least some of the layers of the multilayer planar structure. Thedistributed circuit element is electrically connected to the first radiofrequency port and to the second radio frequency port and is configuredto electrically isolate the antenna from the power source when theantenna is electrically connected to the first radio frequency port andthe radio circuit is electrically connected to the second radiofrequency port.

Various embodiments may realize certain advantages. For example, usingdistributed elements in printed circuit boards to provide high voltageisolation and RF coupling functions avoids the need to use relativelyexpensive high voltage capacitors. Further, the use of printed circuitboard components rather than discrete high voltage capacitors avoids theneed for dielectric overcoatings that is characteristic of certainconventional implementations. As a result, costs may be reduced, andreliability may be improved.

Other features and advantages of the described embodiments may becomeapparent from the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofvarious embodiments, is better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings exemplary embodiments of various aspectsof the invention; however, the invention is not limited to the specificmethods and instrumentalities disclosed. In the drawings:

FIG. 1 is a diagram of an exemplary metering system;

FIG. 2 expands upon the diagram of FIG. 1 and illustrates an exemplarymetering system in greater detail;

FIG. 3A is a block diagram illustrating an exemplary collector;

FIG. 3B is a block diagram illustrating an exemplary meter;

FIG. 4 is a diagram of an exemplary subnet of a wireless network forcollecting data from remote devices;

FIG. 5 is a block diagram illustrating an exemplary utility meteraccording to one embodiment;

FIG. 6 is a schematic diagram illustrating an exemplary antennaisolation circuit according to another embodiment;

FIG. 7 is a plan view of an example printed circuit board layoutimplementing the antenna isolation circuit of FIG. 6;

FIG. 8 is an exploded view of the example printed circuit board layoutof FIG. 7;

FIGS. 9A and 9B are plan and exploded views, respectively, of an exampleprinted circuit board layout implementing another antenna isolationcircuit according to yet another embodiment;

FIG. 10 is a schematic diagram illustrating another exemplary antennaisolation circuit according to still another embodiment;

FIG. 11 is a plan view of an example printed circuit board layoutimplementing the antenna isolation circuit of FIG. 10; and

FIG. 12 is an exploded view of the example printed circuit board layoutof FIG. 11.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Exemplary systems and methods for gathering meter data are describedbelow with reference to FIGS. 1-12. It will be appreciated by those ofordinary skill in the art that the description given herein with respectto those figures is for exemplary purposes only and is not intended inany way to limit the scope of potential embodiments.

Generally, a plurality of meter devices, which operate to track usage ofa service or commodity such as, for example, electricity, water, andgas, are operable to wirelessly communicate. One or more devices,referred to herein as “collectors,” are provided that “collect” datatransmitted by the other meter devices so that it can be accessed byother computer systems. The collectors receive and compile metering datafrom a plurality of meter devices via wireless communications. A datacollection server may communicate with the collectors to retrieve thecompiled meter data.

FIG. 1 provides a diagram of one exemplary metering system 110. System110 comprises a plurality of meters 114, which are operable to sense andrecord consumption or usage of a service or commodity such as, forexample, electricity, water, or gas. Meters 114 may be located atcustomer premises such as, for example, a home or place of business.Meters 114 comprise circuitry for measuring the consumption of theservice or commodity being consumed at their respective locations andfor generating data reflecting the consumption, as well as other datarelated thereto. Meters 114 may also comprise circuitry for wirelesslytransmitting data generated by the meter to a remote location. Meters114 may further comprise circuitry for receiving data, commands orinstructions wirelessly as well. Meters that are operable to bothreceive and transmit data may be referred to as “bi-directional” or“two-way” meters, while meters that are only capable of transmittingdata may be referred to as “transmit-only” or “one-way” meters. Inbi-directional meters, the circuitry for transmitting and receiving maycomprise a transceiver. In an illustrative embodiment, meters 114 maybe, for example, electricity meters manufactured by Elster Electricity,LLC and marketed under the tradename REX.

System 110 further comprises collectors 116. In one embodiment,collectors 116 are also meters operable to detect and record usage of aservice or commodity such as, for example, electricity, water, or gas.In addition, collectors 116 are operable to send data to and receivedata from meters 114. Thus, like the meters 114, the collectors 116 maycomprise both circuitry for measuring the consumption of a service orcommodity and for generating data reflecting the consumption andcircuitry for transmitting and receiving data. In one embodiment,collector 116 and meters 114 communicate with and amongst one anotherusing any one of several wireless techniques such as, for example,frequency hopping spread spectrum (FHSS) and direct sequence spreadspectrum (DSSS).

A collector 116 and the meters 114 with which it communicates define asubnet/LAN 120 of system 110. As used herein, meters 114 and collectors116 may be referred to as “nodes” in the subnet 120. In each subnet/LAN120, each meter transmits data related to consumption of the commoditybeing metered at the meter's location. The collector 116 receives thedata transmitted by each meter 114, effectively “collecting” it, andthen periodically transmits the data from all of the meters in thesubnet/LAN 120 to a data collection server 206. The data collectionserver 206 stores the data for analysis and preparation of bills, forexample. The data collection server 206 may be a specially programmedgeneral purpose computing system and may communicate with collectors 116via a network 112. The network 112 may comprise any form of network,including a wireless network or a fixed-wire network, such as a localarea network (LAN), a wide area network, the Internet, an intranet, atelephone network, such as the public switched telephone network (PSTN),a Frequency Hopping Spread Spectrum (FHSS) radio network, a meshnetwork, a Wi-Fi (802.11) network, a Wi-Max (802.16) network, a landline (POTS) network, or any combination of the above.

Referring now to FIG. 2, further details of the metering system 110 areshown. Typically, the system will be operated by a utility company or acompany providing information technology services to a utility company.As shown, the system 110 comprises a network management server 202, anetwork management system (NMS) 204 and the data collection server 206that together manage one or more subnets/LANs 120 and their constituentnodes. The NMS 204 tracks changes in network state, such as new nodesregistering/unregistering with the system 110, node communication pathschanging, etc. This information is collected for each subnet/LAN 120 andis detected and forwarded to the network management server 202 and datacollection server 206.

Each of the meters 114 and collectors 116 is assigned an identifier (LANID) that uniquely identifies that meter or collector on its subnet/LAN120. In this embodiment, communication between nodes (i.e., thecollectors and meters) and the system 110 is accomplished using the LANID. However, it is preferable for operators of a utility to query andcommunicate with the nodes using their own identifiers. To this end, amarriage file 208 may be used to correlate a utility's identifier for anode (e.g., a utility serial number) with both a manufacturer serialnumber (i.e., a serial number assigned by the manufacturer of the meter)and the LAN ID for each node in the subnet/LAN 120. In this manner, theutility can refer to the meters and collectors by the utilitiesidentifier, while the system can employ the LAN ID for the purpose ofdesignating particular meters during system communications.

A device configuration database 210 stores configuration informationregarding the nodes. For example, in the metering system 200, the deviceconfiguration database may include data regarding time of use (TOU)switchpoints, etc. for the meters 114 and collectors 116 communicatingin the system 110. A data collection requirements database 212 containsinformation regarding the data to be collected on a per node basis. Forexample, a utility may specify that metering data such as load profile,demand, TOU, etc. is to be collected from particular meter(s) 114 a.Reports 214 containing information on the network configuration may beautomatically generated or in accordance with a utility request.

The network management system (NMS) 204 maintains a database describingthe current state of the global fixed network system (current networkstate 220) and a database describing the historical state of the system(historical network state 222). The current network state 220 containsdata regarding current meter-to-collector assignments, etc. for eachsubnet/LAN 120. The historical network state 222 is a database fromwhich the state of the network at a particular point in the past can bereconstructed. The NMS 204 is responsible for, amongst other things,providing reports 214 about the state of the network. The NMS 204 may beaccessed via an API 220 that is exposed to a user interface 216 and aCustomer Information System (CIS) 218. Other external interfaces mayalso be implemented. In addition, the data collection requirementsstored in the database 212 may be set via the user interface 216 or CIS218.

The data collection server 206 collects data from the nodes (e.g.,collectors 116) and stores the data in a database 224. The data includesmetering information, such as energy consumption and may be used forbilling purposes, etc. by a utility provider.

The network management server 202, network management system 204 anddata collection server 206 communicate with the nodes in each subnet/LAN120 via network 110.

FIG. 3A is a block diagram illustrating further details of oneembodiment of a collector 116. Although certain components aredesignated and discussed with reference to FIG. 3A, it should beappreciated that the invention is not limited to such components. Infact, various other components typically found in an electronic metermay be a part of collector 116, but have not been shown in FIG. 3A forthe purposes of clarity and brevity. Also, the invention may use othercomponents to accomplish the operation of collector 116. The componentsthat are shown and the functionality described for collector 116 areprovided as examples, and are not meant to be exclusive of othercomponents or other functionality.

As shown in FIG. 3A, collector 116 may comprise metering circuitry 304that performs measurement of consumption of a service or commodity and aprocessor 305 that controls the overall operation of the meteringfunctions of the collector 116. The collector 116 may further comprise adisplay 310 for displaying information such as measured quantities andmeter status and a memory 312 for storing data. The collector 116further comprises wireless LAN communications circuitry 306 forcommunicating wirelessly with the meters 114 in a subnet/LAN and anetwork interface 308 for communication over the network 112.

In one embodiment, the metering circuitry 304, processor 305, display310 and memory 312 are implemented using an A3 ALPHA meter availablefrom Elster Electricity, Inc. In that embodiment, the wireless LANcommunications circuitry 306 may be implemented by a LAN Option Board(e.g., a 900 MHz two-way radio) installed within the A3 ALPHA meter, andthe network interface 308 may be implemented by a WAN Option Board(e.g., a telephone modem) also installed within the A3 ALPHA meter. Inthis embodiment, the WAN Option Board 308 routes messages from network112 (via interface port 302) to either the meter processor 305 or theLAN Option Board 306. LAN Option Board 306 may use a transceiver (notshown), for example a 900 MHz radio, to communicate data to meters 114.Also, LAN Option Board 306 may have sufficient memory to store datareceived from meters 114. This data may include, but is not limited tothe following: current billing data (e.g., the present values stored anddisplayed by meters 114), previous billing period data, previous seasondata, and load profile data.

LAN Option Board 306 may be capable of synchronizing its time to a realtime clock (not shown) in A3 ALPHA meter, thereby synchronizing the LANreference time to the time in the meter. The processing necessary tocarry out the communication functionality and the collection and storageof metering data of the collector 116 may be handled by the processor305 and/or additional processors (not shown) in the LAN Option Board 306and the WAN Option Board 308.

The responsibility of a collector 116 is wide and varied. Generally,collector 116 is responsible for managing, processing and routing datacommunicated between the collector and network 112 and between thecollector and meters 114. Collector 116 may continually orintermittently read the current data from meters 114 and store the datain a database (not shown) in collector 116. Such current data mayinclude but is not limited to the total kWh usage, the Time-Of-Use (TOU)kWh usage, peak kW demand, and other energy consumption measurements andstatus information. Collector 116 also may read and store previousbilling and previous season data from meters 114 and store the data inthe database in collector 116. The database may be implemented as one ormore tables of data within the collector 116.

FIG. 3B is a block diagram of an exemplary embodiment of a meter 114that may operate in the system 110 of FIGS. 1 and 2. As shown, the meter114 comprises metering circuitry 304′ for measuring the amount of aservice or commodity that is consumed, a processor 305′ that controlsthe overall functions of the meter, a display 310′ for displaying meterdata and status information, and a memory 312′ for storing data andprogram instructions. The meter 114 further comprises wirelesscommunications circuitry 306′ for transmitting and receiving datato/from other meters 114 or a collector 116.

Referring again to FIG. 1, in the exemplary embodiment shown, acollector 116 directly communicates with only a subset of the pluralityof meters 114 in its particular subnet/LAN. Meters 114 with whichcollector 116 directly communicates may be referred to as “level one”meters 114 a. The level one meters 114 a are said to be one “hop” fromthe collector 116. Communications between collector 116 and meters 114other than level one meters 114 a are relayed through the level onemeters 114 a. Thus, the level one meters 114 a operate as repeaters forcommunications between collector 116 and meters 114 located further awayin subnet 120.

Each level one meter 114 a typically will only be in range to directlycommunicate with only a subset of the remaining meters 114 in the subnet120. The meters 114 with which the level one meters 114 a directlycommunicate may be referred to as level two meters 114 b. Level twometers 114 b are one “hop” from level one meters 114 a, and thereforetwo “hops” from collector 116. Level two meters 114 b operate asrepeaters for communications between the level one meters 114 a andmeters 114 located further away from collector 116 in the subnet 120.

While only three levels of meters are shown (collector 116, first level114 a, second level 114 b) in FIG. 1, a subnet 120 may comprise anynumber of levels of meters 114. For example, a subnet 120 may compriseone level of meters but might also comprise eight or more levels ofmeters 114. In an embodiment wherein a subnet comprises eight levels ofmeters 114, as many as 1024 meters might be registered with a singlecollector 116.

As mentioned above, each meter 114 and collector 116 that is installedin the system 110 has a unique identifier (LAN ID) stored thereon thatuniquely identifies the device from all other devices in the system 110.Additionally, meters 114 operating in a subnet 120 comprise informationincluding the following: data identifying the collector with which themeter is registered; the level in the subnet at which the meter islocated; the repeater meter at the prior level with which the metercommunicates to send and receive data to/from the collector; anidentifier indicating whether the meter is a repeater for other nodes inthe subnet; and if the meter operates as a repeater, the identifier thatuniquely identifies the repeater within the particular subnet, and thenumber of meters for which it is a repeater. Collectors 116 have storedthereon all of this same data for all meters 114 that are registeredtherewith. Thus, collector 116 comprises data identifying all nodesregistered therewith as well as data identifying the registered path bywhich data is communicated from the collector to each node. Each meter114 therefore has a designated communications path to the collector thatis either a direct path (e.g., all level one nodes) or an indirect paththrough one or more intermediate nodes that serve as repeaters.

Information is transmitted in this embodiment in the form of packets.For most network tasks such as, for example, reading meter data,collector 116 communicates with meters 114 in the subnet 120 usingpoint-to-point transmissions. For example, a message or instruction fromcollector 116 is routed through the designated set of repeaters to thedesired meter 114. Similarly, a meter 114 communicates with collector116 through the same set of repeaters, but in reverse.

In some instances, however, collector 116 may need to quicklycommunicate information to all meters 114 located in its subnet 120.Accordingly, collector 116 may issue a broadcast message that is meantto reach all nodes in the subnet 120. The broadcast message may bereferred to as a “flood broadcast message.” A flood broadcast originatesat collector 116 and propagates through the entire subnet 120 one levelat a time. For example, collector 116 may transmit a flood broadcast toall first level meters 114 a. The first level meters 114 a that receivethe message pick a random time slot and retransmit the broadcast messageto second level meters 114 b. Any second level meter 114 b can acceptthe broadcast, thereby providing better coverage from the collector outto the end point meters. Similarly, the second level meters 114 b thatreceive the broadcast message pick a random time slot and communicatethe broadcast message to third level meters. This process continues outuntil the end nodes of the subnet. Thus, a broadcast message graduallypropagates outward from the collector to the nodes of the subnet 120.

The flood broadcast packet header contains information to prevent nodesfrom repeating the flood broadcast packet more than once per level. Forexample, within a flood broadcast message, a field might exist thatindicates to meters/nodes which receive the message, the level of thesubnet the message is located; only nodes at that particular level mayre-broadcast the message to the next level. If the collector broadcastsa flood message with a level of 1, only level 1 nodes may respond. Priorto re-broadcasting the flood message, the level 1 nodes increment thefield to 2 so that only level 2 nodes respond to the broadcast.Information within the flood broadcast packet header ensures that aflood broadcast will eventually die out.

Generally, a collector 116 issues a flood broadcast several times, e.g.five times, successively to increase the probability that all meters inthe subnet 120 receive the broadcast. A delay is introduced before eachnew broadcast to allow the previous broadcast packet time to propagatethrough all levels of the subnet.

Meters 114 may have a clock formed therein. However, meters 114 oftenundergo power interruptions that can interfere with the operation of anyclock therein. Accordingly, the clocks internal to meters 114 cannot berelied upon to provide an accurate time reading. Having the correct timeis necessary, however, when time of use metering is being employed.Indeed, in an embodiment, time of use schedule data may also becomprised in the same broadcast message as the time. Accordingly,collector 116 periodically flood broadcasts the real time to meters 114in subnet 120. Meters 114 use the time broadcasts to stay synchronizedwith the rest of the subnet 120. In an illustrative embodiment,collector 116 broadcasts the time every 15 minutes. The broadcasts maybe made near the middle of 15 minute clock boundaries that are used inperforming load profiling and time of use (TOU) schedules so as tominimize time changes near these boundaries. Maintaining timesynchronization is important to the proper operation of the subnet 120.Accordingly, lower priority tasks performed by collector 116 may bedelayed while the time broadcasts are performed.

In an illustrative embodiment, the flood broadcasts transmitting timedata may be repeated, for example, five times, so as to increase theprobability that all nodes receive the time. Furthermore, where time ofuse schedule data is communicated in the same transmission as the timingdata, the subsequent time transmissions allow a different piece of thetime of use schedule to be transmitted to the nodes.

Exception messages are used in subnet 120 to transmit unexpected eventsthat occur at meters 114 to collector 116. In an embodiment, the first 4seconds of every 32-second period are allocated as an exception windowfor meters 114 to transmit exception messages. Meters 114 transmit theirexception messages early enough in the exception window so the messagehas time to propagate to collector 116 before the end of the exceptionwindow. Collector 116 may process the exceptions after the 4-secondexception window. Generally, a collector 116 acknowledges exceptionmessages, and collector 116 waits until the end of the exception windowto send this acknowledgement.

In an illustrative embodiment, exception messages are configured as oneof three different types of exception messages: local exceptions, whichare handled directly by the collector 116 without intervention from datacollection server 206; an immediate exception, which is generallyrelayed to data collection server 206 under an expedited schedule; and adaily exception, which is communicated to the communication server 122on a regular schedule.

Exceptions are processed as follows. When an exception is received atcollector 116, the collector 116 identifies the type of exception thathas been received. If a local exception has been received, collector 116takes an action to remedy the problem. For example, when collector 116receives an exception requesting a “node scan request” such as discussedbelow, collector 116 transmits a command to initiate a scan procedure tothe meter 114 from which the exception was received.

If an immediate exception type has been received, collector 116 makes arecord of the exception. An immediate exception might identify, forexample, that there has been a power outage. Collector 116 may log thereceipt of the exception in one or more tables or files. In anillustrative example, a record of receipt of an immediate exception ismade in a table referred to as the “Immediate Exception Log Table.”Collector 116 then waits a set period of time before taking furtheraction with respect to the immediate exception. For example, collector116 may wait 64 seconds. This delay period allows the exception to becorrected before communicating the exception to the data collectionserver 206. For example, where a power outage was the cause of theimmediate exception, collector 116 may wait a set period of time toallow for receipt of a message indicating the power outage has beencorrected.

If the exception has not been corrected, collector 116 communicates theimmediate exception to data collection server 206. For example,collector 116 may initiate a dial-up connection with data collectionserver 206 and download the exception data. After reporting an immediateexception to data collection server 206, collector 116 may delayreporting any additional immediate exceptions for a period of time suchas ten minutes. This is to avoid reporting exceptions from other meters114 that relate to, or have the same cause as, the exception that wasjust reported.

If a daily exception was received, the exception is recorded in a fileor a database table. Generally, daily exceptions are occurrences in thesubnet 120 that need to be reported to data collection server 206, butare not so urgent that they need to be communicated immediately. Forexample, when collector 116 registers a new meter 114 in subnet 120,collector 116 records a daily exception identifying that theregistration has taken place. In an illustrative embodiment, theexception is recorded in a database table referred to as the “DailyException Log Table.” Collector 116 communicates the daily exceptions todata collection server 206. Generally, collector 116 communicates thedaily exceptions once every 24 hours.

In the present embodiment, a collector assigns designated communicationspaths to meters with bi-directional communication capability, and maychange the communication paths for previously registered meters ifconditions warrant. For example, when a collector 116 is initiallybrought into system 110, it needs to identify and register meters in itssubnet 120. A “node scan” refers to a process of communication between acollector 116 and meters 114 whereby the collector may identify andregister new nodes in a subnet 120 and allow previously registered nodesto switch paths. A collector 116 can implement a node scan on the entiresubnet, referred to as a “full node scan,” or a node scan can beperformed on specially identified nodes, referred to as a “node scanretry.”

A full node scan may be performed, for example, when a collector isfirst installed. The collector 116 must identify and register nodes fromwhich it will collect usage data. The collector 116 initiates a nodescan by broadcasting a request, which may be referred to as a Node ScanProcedure request. Generally, the Node Scan Procedure request directsthat all unregistered meters 114 or nodes that receive the requestrespond to the collector 116. The request may comprise information suchas the unique address of the collector that initiated the procedure. Thesignal by which collector 116 transmits this request may have limitedstrength and therefore is detected only at meters 114 that are inproximity of collector 116. Meters 114 that receive the Node ScanProcedure request respond by transmitting their unique identifier aswell as other data.

For each meter from which the collector receives a response to the NodeScan Procedure request, the collector tries to qualify thecommunications path to that meter before registering the meter with thecollector. That is, before registering a meter, the collector 116attempts to determine whether data communications with the meter will besufficiently reliable. In one embodiment, the collector 116 determineswhether the communication path to a responding meter is sufficientlyreliable by comparing a Received Signal Strength Indication (RSSI) value(i.e., a measurement of the received radio signal strength) measuredwith respect to the received response from the meter to a selectedthreshold value. For example, the threshold value may be −60 dBm. RSSIvalues above this threshold would be deemed sufficiently reliable. Inanother embodiment, qualification is performed by transmitting apredetermined number of additional packets to the meter, such as tenpackets, and counting the number of acknowledgements received back fromthe meter. If the number of acknowledgments received is greater than orequal to a selected threshold (e.g., 8 out of 10), then the path isconsidered to be reliable. In other embodiments, a combination of thetwo qualification techniques may be employed.

If the qualification threshold is not met, the collector 116 may add anentry for the meter to a “Straggler Table.” The entry includes themeter's LAN ID, its qualification score (e.g., 5 out of 10; or its RSSIvalue), its level (in this case level one) and the unique ID of itsparent (in this case the collector's ID).

If the qualification threshold is met or exceeded, the collector 116registers the node. Registering a meter 114 comprises updating a list ofthe registered nodes at collector 116. For example, the list may beupdated to identify the meter's system-wide unique identifier and thecommunication path to the node. Collector 116 also records the meter'slevel in the subnet (i.e. whether the meter is a level one node, leveltwo node, etc.), whether the node operates as a repeater, and if so, thenumber of meters for which it operates as a repeater. The registrationprocess further comprises transmitting registration information to themeter 114. For example, collector 116 forwards to meter 114 anindication that it is registered, the unique identifier of the collectorwith which it is registered, the level the meter exists at in thesubnet, and the unique identifier of its parent meter that will serveras a repeater for messages the meter may send to the collector. In thecase of a level one node, the parent is the collector itself The meterstores this data and begins to operate as part of the subnet byresponding to commands from its collector 116.

Qualification and registration continues for each meter that responds tothe collector's initial Node Scan Procedure request. The collector 116may rebroadcast the Node Scan Procedure additional times so as to insurethat all meters 114 that may receive the Node Scan Procedure have anopportunity for their response to be received and the meter qualified asa level one node at collector 116.

The node scan process then continues by performing a similar process asthat described above at each of the now registered level one nodes. Thisprocess results in the identification and registration of level twonodes. After the level two nodes are identified, a similar node scanprocess is performed at the level two nodes to identify level threenodes, and so on.

Specifically, to identify and register meters that will become level twometers, for each level one meter, in succession, the collector 116transmits a command to the level one meter, which may be referred to asan “Initiate Node Scan Procedure” command. This command instructs thelevel one meter to perform its own node scan process. The requestcomprises several data items that the receiving meter may use incompleting the node scan. For example, the request may comprise thenumber of timeslots available for responding nodes, the unique addressof the collector that initiated the request, and a measure of thereliability of the communications between the target node and thecollector. As described below, the measure of reliability may beemployed during a process for identifying more reliable paths forpreviously registered nodes.

The meter that receives the Initiate Node Scan Response request respondsby performing a node scan process similar to that described above. Morespecifically, the meter broadcasts a request to which all unregisterednodes may respond. The request comprises the number of timeslotsavailable for responding nodes (which is used to set the period for thenode to wait for responses), the unique address of the collector thatinitiated the node scan procedure, a measure of the reliability of thecommunications between the sending node and the collector (which may beused in the process of determining whether a meter's path may beswitched as described below), the level within the subnet of the nodesending the request, and an RSSI threshold (which may also be used inthe process of determining whether a registered meter's path may beswitched). The meter issuing the node scan request then waits for andreceives responses from unregistered nodes. For each response, the meterstores in memory the unique identifier of the responding meter. Thisinformation is then transmitted to the collector.

For each unregistered meter that responded to the node scan issued bythe level one meter, the collector attempts again to determine thereliability of the communication path to that meter. In one embodiment,the collector sends a “Qualify Nodes Procedure” command to the level onenode which instructs the level one node to transmit a predeterminednumber of additional packets to the potential level two node and torecord the number of acknowledgements received back from the potentiallevel two node. This qualification score (e.g., 8 out of 10) is thentransmitted back to the collector, which again compares the score to aqualification threshold. In other embodiments, other measures of thecommunications reliability may be provided, such as an RSSI value.

If the qualification threshold is not met, then the collector adds anentry for the node in the Straggler Table, as discussed above. However,if there already is an entry in the Straggler Table for the node, thecollector will update that entry only if the qualification score forthis node scan procedure is better than the recorded qualification scorefrom the prior node scan that resulted in an entry for the node.

If the qualification threshold is met or exceeded, the collector 116registers the node. Again, registering a meter 114 at level twocomprises updating a list of the registered nodes at collector 116. Forexample, the list may be updated to identify the meter's uniqueidentifier and the level of the meter in the subnet. Additionally, thecollector's 116 registration information is updated to reflect that themeter 114 from which the scan process was initiated is identified as arepeater (or parent) for the newly registered node. The registrationprocess further comprises transmitting information to the newlyregistered meter as well as the meter that will serve as a repeater forthe newly added node. For example, the node that issued the node scanresponse request is updated to identify that it operates as a repeaterand, if it was previously registered as a repeater, increments a dataitem identifying the number of nodes for which it serves as a repeater.Thereafter, collector 116 forwards to the newly registered meter anindication that it is registered, an identification of the collector 116with which it is registered, the level the meter exists at in thesubnet, and the unique identifier of the node that will serve as itsparent, or repeater, when it communicates with the collector 116.

The collector then performs the same qualification procedure for eachother potential level two node that responded to the level one node'snode scan request. Once that process is completed for the first levelone node, the collector initiates the same procedure at each other levelone node until the process of qualifying and registering level two nodeshas been completed at each level one node. Once the node scan procedurehas been performed by each level one node, resulting in a number oflevel two nodes being registered with the collector, the collector willthen send the Initiate Node Scan Response command to each level twonode, in turn. Each level two node will then perform the same node scanprocedure as performed by the level one nodes, potentially resulting inthe registration of a number of level three nodes. The process is thenperformed at each successive node, until a maximum number of levels isreached (e.g., seven levels) or no unregistered nodes are left in thesubnet.

It will be appreciated that in the present embodiment, during thequalification process for a given node at a given level, the collectorqualifies the last “hop” only. For example, if an unregistered noderesponds to a node scan request from a level four node, and therefore,becomes a potential level five node, the qualification score for thatnode is based on the reliability of communications between the levelfour node and the potential level five node (i.e., packets transmittedby the level four node versus acknowledgments received from thepotential level five node), not based on any measure of the reliabilityof the communications over the full path from the collector to thepotential level five node. In other embodiments, of course, thequalification score could be based on the full communication path.

At some point, each meter will have an established communication path tothe collector which will be either a direct path (i.e., level one nodes)or an indirect path through one or more intermediate nodes that serve asrepeaters. If during operation of the network, a meter registered inthis manner fails to perform adequately, it may be assigned a differentpath or possibly to a different collector as described below.

As previously mentioned, a full node scan may be performed when acollector 116 is first introduced to a network. At the conclusion of thefull node scan, a collector 116 will have registered a set of meters 114with which it communicates and reads metering data. Full node scansmight be periodically performed by an installed collector to identifynew meters 114 that have been brought on-line since the last node scanand to allow registered meters to switch to a different path.

In addition to the full node scan, collector 116 may also perform aprocess of scanning specific meters 114 in the subnet 120, which isreferred to as a “node scan retry.” For example, collector 116 may issuea specific request to a meter 114 to perform a node scan outside of afull node scan when on a previous attempt to scan the node, thecollector 116 was unable to confirm that the particular meter 114received the node scan request. Also, a collector 116 may request a nodescan retry of a meter 114 when during the course of a full node scan thecollector 116 was unable to read the node scan data from the meter 114.Similarly, a node scan retry will be performed when an exceptionprocedure requesting an immediate node scan is received from a meter114.

The system 110 also automatically reconfigures to accommodate a newmeter 114 that may be added. More particularly, the system identifiesthat the new meter has begun operating and identifies a path to acollector 116 that will become responsible for collecting the meteringdata. Specifically, the new meter will broadcast an indication that itis unregistered. In one embodiment, this broadcast might be, forexample, embedded in, or relayed as part of a request for an update ofthe real time as described above. The broadcast will be received at oneof the registered meters 114 in proximity to the meter that isattempting to register. The registered meter 114 forwards the time tothe meter that is attempting to register. The registered node alsotransmits an exception request to its collector 116 requesting that thecollector 116 implement a node scan, which presumably will locate andregister the new meter. The collector 116 then transmits a request thatthe registered node perform a node scan. The registered node willperform the node scan, during which it requests that all unregisterednodes respond. Presumably, the newly added, unregistered meter willrespond to the node scan. When it does, the collector will then attemptto qualify and then register the new node in the same manner asdescribed above.

Once a communication path between the collector and a meter isestablished, the meter can begin transmitting its meter data to thecollector and the collector can transmit data and instructions to themeter. As mentioned above, data is transmitted in packets. “Outbound”packets are packets transmitted from the collector to a meter at a givenlevel. In one embodiment, outbound packets contain the following fields,but other fields may also be included:

-   Length—the length of the packet;-   SrcAddr—source address—in this case, the ID of the collector;-   DestAddr—the LAN ID of the meter to which the packet addressed;    -   RptPath—the communication path to the destination meter (i.e.,        the list of identifiers of each repeater in the path from the        collector to the destination node); and    -   Data—the payload of the packet.        The packet may also include integrity check information (e.g.,        CRC), a pad to fill-out unused portions of the packet and other        control information. When the packet is transmitted from the        collector, it will only be forwarded on to the destination meter        by those repeater meters whose identifiers appear in the RptPath        field. Other meters that may receive the packet, but that are        not listed in the path identified in the RptPath field will not        repeat the packet.

“Inbound” packets are packets transmitted from a meter at a given levelto the collector. In one embodiment, inbound packets contain thefollowing fields, but other fields may also be included:

-   Length—the length of the packet;-   SrcAddr—source address—the address of the meter that initiated the    packet;-   DestAddr—the ID of the collector to which the packet is to be    transmitted;    -   RptAddr—the ID of the parent node that serves as the next        repeater for the sending node;    -   Data—the payload of the packet;        Because each meter knows the identifier of its parent node        (i.e., the node in the next lower level that serves as a        repeater for the present node), an inbound packet need only        identify who is the next parent. When a node receives an inbound        packet, it checks to see if the RptAddr matches its own        identifier. If not, it discards the packet. If so, it knows that        it is supposed to forward the packet on toward the collector.        The node will then replace the RptAddr field with the identifier        of its own parent and will then transmit the packet so that its        parent will receive it. This process will continue through each        repeater at each successive level until the packet reaches the        collector.

For example, suppose a meter at level three initiates transmission of apacket destined for its collector. The level three node will insert inthe RptAddr field of the inbound packet the identifier of the level twonode that serves as a repeater for the level three node. The level threenode will then transmit the packet. Several level two nodes may receivethe packet, but only the level two node having an identifier thatmatches the identifier in the RptAddr field of the packet willacknowledge it. The other will discard it. When the level two node withthe matching identifier receives the packet, it will replace the RptAddrfield of the packet with the identifier of the level one packet thatserves as a repeater for that level two packet, and the level two packetwill then transmit the packet. This time, the level one node having theidentifier that matches the RptAddr field will receive the packet. Thelevel one node will insert the identifier of the collector in theRptAddr field and will transmit the packet. The collector will thenreceive the packet to complete the transmission.

A collector 116 periodically retrieves meter data from the meters thatare registered with it. For example, meter data may be retrieved from ameter every 4 hours. Where there is a problem with reading the meterdata on the regularly scheduled interval, the collector will try to readthe data again before the next regularly scheduled interval.Nevertheless, there may be instances wherein the collector 116 is unableto read metering data from a particular meter 114 for a prolonged periodof time. The meters 114 store an indication of when they are read bytheir collector 116 and keep track of the time since their data has lastbeen collected by the collector 116. If the length of time since thelast reading exceeds a defined threshold, such as for example, 18 hours,presumably a problem has arisen in the communication path between theparticular meter 114 and the collector 116. Accordingly, the meter 114changes its status to that of an unregistered meter and attempts tolocate a new path to a collector 116 via the process described above fora new node. Thus, the exemplary system is operable to reconfigure itselfto address inadequacies in the system.

In some instances, while a collector 116 may be able to retrieve datafrom a registered meter 114 occasionally, the level of success inreading the meter may be inadequate. For example, if a collector 116attempts to read meter data from a meter 114 every 4 hours but is ableto read the data, for example, only 70 percent of the time or less, itmay be desirable to find a more reliable path for reading the data fromthat particular meter. Where the frequency of reading data from a meter114 falls below a desired success level, the collector 116 transmits amessage to the meter 114 to respond to node scans going forward. Themeter 114 remains registered but will respond to node scans in the samemanner as an unregistered node as described above. In other embodiments,all registered meters may be permitted to respond to node scans, but ameter will only respond to a node scan if the path to the collectorthrough the meter that issued the node scan is shorter (i.e., less hops)than the meter's current path to the collector. A lesser number of hopsis assumed to provide a more reliable communication path than a longerpath. A node scan request always identifies the level of the node thattransmits the request, and using that information, an already registerednode that is permitted to respond to node scans can determine if apotential new path to the collector through the node that issued thenode scan is shorter than the node's current path to the collector.

If an already registered meter 114 responds to a node scan procedure,the collector 116 recognizes the response as originating from aregistered meter but that by re-registering the meter with the node thatissued the node scan, the collector may be able to switch the meter to anew, more reliable path. The collector 116 may verify that the RSSIvalue of the node scan response exceeds an established threshold. If itdoes not, the potential new path will be rejected. However, if the RSSIthreshold is met, the collector 116 will request that the node thatissued the node scan perform the qualification process described above(i.e., send a predetermined number of packets to the node and count thenumber of acknowledgements received). If the resulting qualificationscore satisfies a threshold, then the collector will register the nodewith the new path. The registration process comprises updating thecollector 116 and meter 114 with data identifying the new repeater (i.e.the node that issued the node scan) with which the updated node will nowcommunicate. Additionally, if the repeater has not previously performedthe operation of a repeater, the repeater would need to be updated toidentify that it is a repeater. Likewise, the repeater with which themeter previously communicated is updated to identify that it is nolonger a repeater for the particular meter 114. In other embodiments,the threshold determination with respect to the RSSI value may beomitted. In such embodiments, only the qualification of the last “hop”(i.e., sending a predetermined number of packets to the node andcounting the number of acknowledgements received) will be performed todetermine whether to accept or reject the new path.

In some instances, a more reliable communication path for a meter mayexist through a collector other than that with which the meter isregistered. A meter may automatically recognize the existence of themore reliable communication path, switch collectors, and notify theprevious collector that the change has taken place. The process ofswitching the registration of a meter from a first collector to a secondcollector begins when a registered meter 114 receives a node scanrequest from a collector 116 other than the one with which the meter ispresently registered. Typically, a registered meter 114 does not respondto node scan requests. However, if the request is likely to result in amore reliable transmission path, even a registered meter may respond.Accordingly, the meter determines if the new collector offers apotentially more reliable transmission path. For example, the meter 114may determine if the path to the potential new collector 116 comprisesfewer hops than the path to the collector with which the meter isregistered. If not, the path may not be more reliable and the meter 114will not respond to the node scan. The meter 114 might also determine ifthe RSSI of the node scan packet exceeds an RSSI threshold identified inthe node scan information. If so, the new collector may offer a morereliable transmission path for meter data. If not, the transmission pathmay not be acceptable and the meter may not respond. Additionally, ifthe reliability of communication between the potential new collector andthe repeater that would service the meter meets a threshold establishedwhen the repeater was registered with its existing collector, thecommunication path to the new collector may be more reliable. If thereliability does not exceed this threshold, however, the meter 114 doesnot respond to the node scan.

If it is determined that the path to the new collector may be betterthan the path to its existing collector, the meter 114 responds to thenode scan. Included in the response is information regarding any nodesfor which the particular meter may operate as a repeater. For example,the response might identify the number of nodes for which the meterserves as a repeater.

The collector 116 then determines if it has the capacity to service themeter and any meters for which it operates as a repeater. If not, thecollector 116 does not respond to the meter that is attempting to changecollectors. If, however, the collector 116 determines that it hascapacity to service the meter 114, the collector 116 stores registrationinformation about the meter 114. The collector 116 then transmits aregistration command to meter 114. The meter 114 updates itsregistration data to identify that it is now registered with the newcollector. The collector 116 then communicates instructions to the meter114 to initiate a node scan request. Nodes that are unregistered, orthat had previously used meter 114 as a repeater respond to the requestto identify themselves to collector 116. The collector registers thesenodes as is described above in connection with registering newmeters/nodes.

Under some circumstances it may be necessary to change a collector. Forexample, a collector may be malfunctioning and need to be takenoff-line. Accordingly, a new communication path must be provided forcollecting meter data from the meters serviced by the particularcollector. The process of replacing a collector is performed bybroadcasting a message to unregister, usually from a replacementcollector, to all of the meters that are registered with the collectorthat is being removed from service. In one embodiment, registered metersmay be programmed to only respond to commands from the collector withwhich they are registered. Accordingly, the command to unregister maycomprise the unique identifier of the collector that is being replaced.In response to the command to unregister, the meters begin to operate asunregistered meters and respond to node scan requests. To allow theunregistered command to propagate through the subnet, when a nodereceives the command it will not unregister immediately, but ratherremain registered for a defined period, which may be referred to as the“Time to Live”. During this time to live period, the nodes continue torespond to application layer and immediate retries allowing theunregistration command to propagate to all nodes in the subnet.Ultimately, the meters register with the replacement collector using theprocedure described above.

One of collector's 116 main responsibilities within subnet 120 is toretrieve metering data from meters 114. In one embodiment, collector 116has as a goal to obtain at least one successful read of the meteringdata per day from each node in its subnet. Collector 116 attempts toretrieve the data from all nodes in its subnet 120 at a configurableperiodicity. For example, collector 116 may be configured to attempt toretrieve metering data from meters 114 in its subnet 120 once every 4hours. In greater detail, in one embodiment, the data collection processbegins with the collector 116 identifying one of the meters 114 in itssubnet 120. For example, collector 116 may review a list of registerednodes and identify one for reading. The collector 116 then communicatesa command to the particular meter 114 that it forward its metering datato the collector 116. If the meter reading is successful and the data isreceived at collector 116, the collector 116 determines if there areother meters that have not been read during the present reading session.If so, processing continues. However, if all of the meters 114 in subnet120 have been read, the collector waits a defined length of time, suchas, for example, 4 hours, before attempting another read.

If during a read of a particular meter, the meter data is not receivedat collector 116, the collector 116 begins a retry procedure wherein itattempts to retry the data read from the particular meter. Collector 116continues to attempt to read the data from the node until either thedata is read or the next subnet reading takes place. In an embodiment,collector 116 attempts to read the data every 60 minutes. Thus, whereina subnet reading is taken every 4 hours, collector 116 may issue threeretries between subnet readings.

Meters 114 are often two-way meters—i.e. they are operable to bothreceive and transmit data. However, one-way meters that are operableonly to transmit and not receive data may also be deployed. FIG. 4 is ablock diagram illustrating a subnet 401 that includes a number ofone-way meters 451-456. As shown, meters 114 a-k are two-way devices. Inthis example, the two-way meters 114 a-k operate in the exemplary mannerdescribed above, such that each meter has a communication path to thecollector 116 that is either a direct path (e.g., meters 114 a and 114 bhave a direct path to the collector 116) or an indirect path through oneor more intermediate meters that serve as repeaters. For example, meter114 h has a path to the collector through, in sequence, intermediatemeters 114 d and 114 b. In this example embodiment, when a one-way meter(e.g., meter 451) broadcasts its usage data, the data may be received atone or more two-way meters that are in proximity to the one-way meter(e.g., two-way meters 114 f and 114 g). In one embodiment, the data fromthe one-way meter is stored in each two-way meter that receives it, andthe data is designated in those two-way meters as having been receivedfrom the one-way meter. At some point, the data from the one-way meteris communicated, by each two-way meter that received it, to thecollector 116. For example, when the collector reads the two-way meterdata, it recognizes the existence of meter data from the one-way meterand reads it as well. After the data from the one-way meter has beenread, it is removed from memory.

While the collection of data from one-way meters by the collector hasbeen described above in the context of a network of two-way meters 114that operate in the manner described in connection with the embodimentsdescribed above, it is understood that the present invention is notlimited to the particular form of network established and utilized bythe meters 114 to transmit data to the collector. Rather, the presentinvention may be used in the context of any network topology in which aplurality of two-way communication nodes are capable of transmittingdata and of having that data propagated through the network of nodes tothe collector.

According to various embodiments, a planar antenna isolation circuituses distributed elements to provide high voltage isolation and RFcoupling functions. The distributed elements may be implemented, forexample, as multilayer distributed capacitors. In other embodiments, thedistributed elements may be implemented as a distributed transformer.

FIG. 5 is a block diagram illustrating an exemplary utility meter 500according to one embodiment. The utility meter 500 receives power from apower source, such as an alternating current (AC) power supply 502, andincludes metering and control circuitry 504, which both measuresconsumption of a resource and controls the operation of the utilitymeter 500. In some embodiments, the metering and control circuitry 504measures consumption of electricity. In other embodiments, however, themetering and control circuitry 504 may be configured to measureconsumption of another type of resource, such as, for example, water ornatural gas. The metering and control circuitry 504 may be integratedinto a single module, as shown in FIG. 5. Alternatively, the meteringand control functionality may be separated between two or more circuitsor modules. A radio transceiver 506 is electrically connected to themetering and control circuitry 504 and generates a signal that is basedon the consumption of the electricity or other resource as measured bythe metering and control circuitry 504. An antenna 508 operativelycoupled to the radio transceiver 506 emits the signal that is generatedby the metering and control circuitry 504. The antenna 508 is connectedto an earth ground 510 and may also be connected to an additionaloptional ground 512.

An antenna isolation circuit 514 is electrically connected both to theradio transceiver 506 and to the antenna 508. As discussed in greaterdetail below in connection with various embodiments, the planar antennaisolation circuit 514 is formed by multiple conductive layers separatedby a dielectric material. Respective conductive traces are on at leastsome of the layers. A distributed circuit element is formed by theconductive traces of at least some of the layers of the planar medium,and is electrically connected both to the radio transceiver 506 and tothe antenna 508. The distributed circuit element electrically isolatesthe antenna 508 from the AC power supply 502. In this way, a user whotouches the antenna 508 during operation is protected from exposure tothe line voltage from the AC power supply 502. In addition, the internalcomponents of the utility meter 500, such as the metering and controlcircuitry 504 and the radio transceiver 506, are protected fromelectrical discharges to the antenna 508, e.g., during electricalstorms. In some embodiments, the utility meter 500 may also incorporatea display 516 that renders a visual representation of the consumption ofthe electricity or other resource as measured by the metering andcontrol circuitry 504.

FIG. 6 is a block diagram illustrating an exemplary antenna isolationcircuit 600 according to another embodiment. In the embodiment shown inFIG. 6, the antenna isolation circuit 600 is formed by two capacitors602 and 604 and a resonant stub 606. It will be appreciated by thoseskilled in the art that the antenna isolation circuit 600 mayincorporate more or fewer capacitors than are depicted in FIG. 6. Thecapacitors 602 and 604 are implemented as multilayer distributedcapacitors, and the resonant stub 606 is implemented as a spiral stub.The capacitors 602 and 604 provide high voltage isolation and a lowimpedance RF path between a radio RF connection 608 and an antenna RFconnection 610. The resonant stub 606 presents a low impedance totransients across the radio RF connection 608, while remainingessentially transparent to the desired RF signals.

The antenna isolation circuit 600 has a relatively low impedance betweenthe radio RF connection 608 and the antenna RF connection 610.Accordingly, the antenna isolation circuit 600 is suitable forinstallation in operating environments that are characterized byrelatively long runs of coaxial cable between the antenna and theantenna RF connection 610.

FIG. 7 is a plan view of an example printed circuit board layout 700implementing the antenna isolation circuit 600 of FIG. 6. The printedcircuit board layout 700 is formed from multiple layers of circuittraces separated by dielectric material. The printed circuit boardlayout 700 includes an antenna RF connection 702, which may be connectedto an antenna cable 704 that is in turn connected to an antenna (notshown), as shown in FIG. 7. Alternatively, the antenna RF connection 702may be connected directly to an antenna (not shown). The printed circuitboard layout 700 also includes a radio RF connection 706 that isconnected to a radio circuit, e.g., the radio transceiver 506 of FIG. 5or another internal component of the utility meter 500. As shown ingreater detail in FIG. 8, multilayer capacitors 708, 710, and 712 areformed by circuit traces of multiple layers of the printed circuit boardlayout 700. The multilayer capacitors 708, 710, and 712 provide highvoltage isolation and a low impedance RF path between the antenna RFconnection 702 and the radio RF connection 706. A spiral stub 714 formedon one of the layers of the printed circuit board layout 700 provides alow impedance to transients across the radio RF connection 706, whileremaining essentially transparent to desired RF signals.

FIG. 8 is an exploded view of the example printed circuit board layout700 of FIG. 7. As shown in FIG. 8, the printed circuit board layout 700includes four layers 800, 802, 804, and 806. The layers 800, 802, 804,and 806 are separated from one another by dielectric material, which isnot shown in the exploded view of FIG. 8. The layers are connectedtogether at the RF and antenna connection ends by plated through viaholes, shown as small white circles in printed circuit trace patterns.The layer 800 includes a circuit trace 808 forming a first layer ofcapacitors 708, 710, and 712 of FIG. 7. In addition, the spiral stub 714of FIG. 7 is formed on the circuit trace 808. Portions of the antenna RFconnection 702 and of the radio RF connection 706 are also formed on thecircuit trace 808. The layer 802 is located under the layer 800 andincludes a circuit trace 810 that forms a second layer of capacitors708, 710, and 712. The layer 804 is located under the layer 802 andincludes a circuit trace 812 that forms a third layer of capacitors 708,710, and 712. The layer 806 is located under the layer 804 and includesa circuit trace 814 that forms a fourth layer of capacitors 708, 710,and 712. In addition, the circuit trace 814 forms part of the antenna RFconnection 702 and part of the radio RF connection 706.

Planar electromagnetic design simulation results have been obtained forthe printed circuit board layout 700. To reduce what could otherwise bea lengthy simulation time, three frequencies in a range of interest wereselected: 890 MHz, 915 MHz, and 940 MHz. For each frequency, the returnloss and insertion loss for the printed circuit board layout weresimulated. The simulation results are presented below in Table 1.

TABLE 1 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −30.34−0.14 915 −34.11 −0.14 940 −40.55 −0.15

In addition, a sample circuit board embodying the printed circuit boardlayout 700 was built, and the return loss and insertion loss weremeasured over a range of frequencies. Table 2, below, presents examplemeasured return loss and insertion loss values for similar frequenciesas were simulated.

TABLE 2 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −21.23−0.45 915 −21.55 −0.42 940 −21.44 −0.42Both the simulated and measured results met or exceeded designspecifications. It will be appreciated that the measured insertion lossvalues include insertion losses from the RF connectors used formeasurement at the receiver and antenna RF connection points, whichcontribute a total of approximately −0.3 dB for both connectors. Thedifferences between the measured and simulated return losses were wellwithin the expected ranges as the RF connectors were included in themeasurements and not in the simulations. Also, return loss is aninherently sensitive parameter that is subject to significantcomputational errors for complex electromagnetic simulation problems,particularly for small values on the order of −25 dB or lower.

FIGS. 9A and 9B are plan and exploded views, respectively, of an exampleprinted circuit board layout implementing another antenna isolationcircuit 900 according to yet another embodiment. The antenna isolationcircuit 900 is similar in some respects to the antenna isolation circuit600. In particular, the antenna isolation circuit 900 employs adistributed capacitor design. Unlike the antenna isolation circuit 600,however, the antenna isolation circuit 900 uses an asymmetrical design,incorporating a single capacitor 902 in a main RF path and a largercapacitor 904 (not visible in FIG. 9A) in a ground return path between aradio RF connection 906 and an antenna RF coaxial connection 908. Theantenna isolation circuit 900 also incorporates a spiral resonant stub910 at the radio RF connection 906 for ESD/transient protection.Connections between layers are formed by plated through via holes, shownas small white circles in printed circuit trace patterns. Thisembodiment results in a more compact design than the antenna isolationcircuit 600 due to the reduced number of capacitors, and supports anirregular PCB outline and an unusual antenna port RF coaxial portorientation. Certain space constrained applications may benefit fromsuch characteristics.

FIG. 10 is a schematic diagram illustrating another exemplary antennaisolation circuit 1000 according to still another embodiment. Theantenna isolation circuit 1000 employs a distributed transformer designthat provides voltage isolation, low loss RF coupling, and ESDprotection in a single multilayer printed circuit board structure. Theantenna isolation circuit 1000 includes a radio RF connection 1002,which may be connected to a radio circuit, e.g., the radio transceiver506 of FIG. 5 or another internal component of the utility meter 500. Anantenna RF connection 1004 may be connected to an antenna cable that isin turn connected to an antenna or may be connected directly to anantenna. A printed circuit board transformer 1006 is connected betweenthe radio RF connection 1002 and the antenna RF connection 1004. Theprinted board transformer 1006 includes a primary winding 1008 and asecondary winding 1010, which are identical in the embodiment shown inFIG. 10. The entire structure is electrically symmetrical, allowingtransposition of the radio RF connection 1002 and the antenna RFconnection 1004 with no effects on performance.

The antenna isolation circuit 1000 is a quasi-balanced structure.Accordingly, the common mode impedance between the radio RF connection1002 and the antenna RF connection 1004 is high relative to that of acapacitively coupled structure. Thus, the antenna isolation circuit 1000is suitable for installation close to an antenna, or with the antennalocated remotely and connected to the antenna isolation circuit 1000 viaa common high mode impedance transmission line, e.g., a ferrite loadedantenna cable. The antenna isolation circuit 1000 is also suitable forinstallation in operating environments characterized by a balancedtransmission line feed.

FIG. 11 is a plan view of an example printed circuit board layout 1100implementing the antenna isolation circuit 1000 of FIG. 10. The printedcircuit board layout 1100 is formed from multiple layers of circuittraces separated by dielectric material. The printed circuit boardlayout 1100 includes an antenna coaxial connection 1102, which may beconnected to an antenna cable that is in turn connected to an antenna.Alternatively, the antenna coaxial connection 1102 may be connecteddirectly to the antenna. The printed circuit board layout 1100 alsoincludes a radio RF connection 1104 that is connected to a radiocircuit, e.g., the radio transceiver 506 of FIG. 5 or another internalcomponent of the utility meter 500. As shown in greater detail in FIG.12, a multilayer transformer 1106 is formed by circuit traces ofmultiple layers of the printed circuit board layout 1100. In particular,the multilayer transformer 1100 includes a primary winding and asecondary winding formed by circuit traces of alternating layers of theprinted circuit board layout 1100. The multilayer transformer 1100transfers RF energy between the antenna coaxial connection 1102 and theradio RF connection 1104, while providing ESD/transient protection atboth the antenna coaxial connection 1102 and the radio RF connection1104.

FIG. 12 is an exploded view of the example printed circuit board layout1100 of FIG. 11. As shown in FIG. 12, the printed circuit board layout1100 includes four layers 1200, 1202, 1204, and 1206. The layers 1200,1202, 1204, and 1206 are separated from one another by dielectricmaterial, which is not shown in the exploded view of FIG. 12. The layersare connected together at the RF and antenna connection ends by platedvia holes, shown as small white circles in printed circuit tracepatterns. The layer 1200 includes a circuit trace 1208 forming a firstportion 1210 of the secondary winding 1010 of FIG. 10. In addition,portions of the antenna coaxial connection 1102 and of the radio RFconnection 1104 are formed on the circuit trace 1208. The layer 1202 islocated under the layer 1200 and includes a circuit trace 1212 thatforms a first portion 1214 of the primary winding 1008 of FIG. 10. Thelayer 1204 is located under the layer 1202 and includes a circuit trace1216 that forms a second portion 1218 of the secondary winding 1010. Thelayer 1206 is located under the layer 1204 and includes a circuit trace1220 that forms a second portion 1222 of the primary winding 1008. Inaddition, the circuit trace 1220 forms part of the antenna coaxialconnection 1102 and part of the radio RF connection 1104.

Planar electromagnetic design simulation results have been obtained forthe printed circuit board layout 1100. To reduce what could otherwise bea lengthy simulation time, three frequencies in a range of interest wereselected: 890 MHz, 915 MHz, and 940 MHz. For each frequency, the returnloss and insertion loss for the printed circuit board layout weresimulated. Simulation results were obtained for a first examplestructure that was optimized for RF performance at frequencies below 890MHz and for a second example structure that was optimized for RFperformance in the 902-928 MHz ISM frequency band. The simulationresults for the first example structure, which was optimized for RFperformance at frequencies below 890 MHz, are presented below in Table3.

TABLE 3 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −35.53−0.17 915 −31.74 −0.17 940 −25.49 −0.18The simulation results for the second example structure, which wasoptimized for RF performance in the 902-928 MHz ISM frequency band, arepresented below in Table 4.

TABLE 4 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −29.51−0.16 915 −37.57 −0.16 940 −32.11 −0.16

In addition, a number of sample circuit boards embodying the printedcircuit board layout 1100 were built, and the return loss and insertionloss were measured over a range of frequencies. Some sample circuitboards were built that were optimized for RF performance at frequenciesbelow 890 MHz. Other sample circuit boards were built that wereoptimized for RF performance in the 902-928 MHz ISM frequency band.Table 5, below, presents example measured return loss and insertion lossvalues for similar frequencies as were simulated for an example circuitboard that was optimized for RF performance at frequencies below 890MHz.

TABLE 5 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −24.11−0.51 915 −22.39 −0.53 940 −22.13 −0.51Table 6, below, presents example measured return loss and insertion lossvalues for similar frequencies as were simulated for an example circuitboard that was optimized for RF performance at frequencies in the902-928 MHz ISM frequency band.

TABLE 6 Frequency (MHz) Return Loss (dB) Insertion Loss (dB) 890 −37.08−0.45 915 −46.8 −0.46 940 −39.32 −0.46Both the simulated and measured results met or exceeded designspecifications. It will be appreciated that the measured insertion lossvalues include insertion losses from the RF connectors used formeasurement at the receiver and antenna RF connection points, whichcontribute a total of approximately −0.3 dB for both connectors. Thedifferences between the measured and simulated return losses were wellwithin the expected ranges as the RF connectors were included in themeasurements and not in the simulations. Also, return loss is aninherently sensitive parameter that is subject to significantcomputational errors for complex electromagnetic simulation problems,particularly for small values on the order of −25 dB or lower.

While systems and methods have been described and illustrated withreference to specific embodiments, those skilled in the art willrecognize that modification and variations may be made without departingfrom the principles described above and set forth in the followingclaims. For example, although in the embodiments described above,particular circuit board layouts are illustrated in the Figures anddescribed in the Specification, it will be appreciated that otherlayouts can be implemented, e.g., incorporating more or fewer capacitorsor transformers, consistent with the principles disclosed herein.Additionally, the implementation medium is not limited to conventionalPCB material (e.g., thin copper conducting surfaces separated by fiberepoxy or homogeneous dielectric material). Certain embodiments mayincorporate conductive layers separated by a rigid dielectric material,such as ceramic (e.g., alumina or zirconium tin titanate), glass, ordiamond. Other embodiments may incorporate conductive layers separatedby a flexible dielectric material such as polyimide film. The number ofconductive layers comprising the structure may range from two to anylarger value, within the constraints of practical implementation.Accordingly, reference should be made to the following claims asdescribing the scope of the present invention.

1. An antenna isolation circuit comprising: a multilayer planarstructure comprising at least two conductive layers separated from oneanother by a dielectric material; a first radio frequency portelectrically connected to the multilayer planar structure, the firstradio frequency port arranged to be electrically connected to anantenna; a second radio frequency port electrically connected to themultilayer planar structure, the second radio frequency port arranged tobe electrically connected to a radio circuit receiving power from apower source; and a distributed circuit element electrically connectedto the first radio frequency port and to the second radio frequency portand comprising at least some of the conductive layers of the multilayerplanar structure, wherein the distributed circuit element is configuredto electrically isolate the antenna from the power source when theantenna is electrically connected to the first radio frequency port andthe radio circuit is electrically connected to the second radiofrequency port.
 2. The antenna isolation circuit of claim 1, wherein thedistributed circuit element comprises a capacitor.
 3. The antennaisolation circuit of claim 2, wherein the distributed circuit elementfurther comprises a resonant stub formed by one of the conductive layersof the multilayer planar structure.
 4. The antenna isolation circuit ofclaim 3, wherein the resonant stub comprises a spiral stub.
 5. Theantenna isolation circuit of claim 1, wherein the distributed circuitelement comprises a quasi-balanced transformer.
 6. The antenna isolationcircuit of claim 5, wherein the quasi-balanced transformer comprises: aprimary winding comprising respective first conductive layers of a firstsubset of the conductive layers of the multilayer planar structure; anda secondary winding comprising respective second conductive layers of asecond subset of the conductive layers of the multilayer planarstructure.
 7. The antenna isolation circuit of claim 6, wherein therespective first conductive layers and the respective second conductivelayers have loop portions having substantially identical dimensions. 8.A meter reading device comprising: a power source; a metering circuitconfigured to measure consumption of a resource; a transceiverelectrically connected to the metering circuit and configured togenerate a signal based on the measured consumption of the resource; anantenna operatively coupled to the transceiver and configured to emitthe generated signal; and an antenna isolation circuit electricallyconnected to the transceiver and to the antenna, the antenna isolationcircuit comprising a multilayer planar structure comprising a pluralityof layers, at least some of the layers of the printed circuit boardincluding respective conductive traces, a dielectric material separatingeach of the plurality of layers, and distributed circuit elementselectrically connected to the transceiver and to the antenna andcomprising the respective conductive traces of at least some of thelayers of the multilayer planar structure, wherein the distributedcircuit element is configured to electrically isolate the antenna fromthe power source.
 9. The meter reading device of claim 8, wherein thedistributed circuit element comprises a capacitor.
 10. The meter readingdevice of claim 9, wherein the distributed circuit element furthercomprises a resonant stub formed on a conductive trace on one of thelayers of the multilayer planar structure.
 11. The meter reading deviceof claim 8, wherein the distributed circuit element comprises aquasi-balanced transformer.
 12. The meter reading device of claim 11,wherein the quasi-balanced transformer comprises: a primary windingcomprising respective conductive traces of respective first layers of afirst subset of the layers of the multilayer planar structure; and asecondary winding comprising respective printed conductive traces ofrespective second layers of a second subset of the layers of themultilayer planar structure.
 13. The meter reading device of claim 12,wherein the respective conductive traces of the respective first layersand of the respective second layers have loop portions havingsubstantially identical dimensions.
 14. The meter reading device ofclaim 8, further comprising a display operatively coupled to themetering circuit.
 15. A method of manufacturing an antenna isolationcircuit, the method comprising: providing a multilayer planar structurecomprising a plurality of conductive layers separated by a dielectricmaterial; providing a first radio frequency port electrically connectedto the multilayer planar structure, the first radio frequency portarranged to be electrically connected to an antenna; providing a secondradio frequency port electrically connected to the multilayer planarstructure, the second radio frequency port arranged to be electricallyconnected to a radio circuit; forming a distributed circuit element as aplurality of conductive traces on at least some of the layers of themultilayer planar structure, the distributed circuit elementelectrically connected to the first radio frequency port and to thesecond radio frequency port and configured to electrically isolate theantenna from the power source when the antenna is electrically connectedto the first radio frequency port and the radio circuit is electricallyconnected to the second radio frequency port.
 16. The method of claim15, wherein forming the distributed circuit element comprises forming acapacitor.
 17. The method of claim 16, wherein forming the distributedcircuit element comprises forming a resonant stub on one of the printedcircuit board traces.
 18. The method of claim 15, wherein forming thedistributed circuit element comprises forming a quasi-balancedtransformer.
 19. The method of claim 18, wherein forming thequasi-balanced transformer comprises: forming a primary windingcomprising respective conductive traces on respective first layers of afirst subset of the layers of the multilayer planar structure; andforming a secondary winding comprising respective conductive traces onrespective second layers of a second subset of the layers of themultilayer planar structure.
 20. The method of claim 19, wherein therespective conductive traces of the respective first layers and of therespective second layers have loop portions having substantiallyidentical dimensions.